The present invention relates to qualifying heads for storage devices. In particular, the present invention relates to qualifying heads based on the PES linearity produced by the head.
In mass storage devices with movable heads, the position of the head is determined based on a position error signal (PES), which is generated from one or more servo fields on the storage medium. Ideally, the PES is a linear function of head position. In actual drives, many factors can adversely affect the linearity of the PES.
One of the major causes of non-linearity in the PES is the performance of the head. In the past, the benchmark for determining whether a head would produce a linear PES has been the reader width of the head. In the past, if the reader width was below 45 percent of the nominal track width for the medium or some other minimum reader width specification, the head was assumed to provide a nonlinear PES and was rejected.
With every new generation of disc drives, the track width on the medium decreases. This reduction in track width can only be achieved with a similar reduction in the size of the head. However, as head sizes have decreased, the ability to manufacture the head within tolerances has been reduced. Because of this, when a batch of heads is produced, more of the heads fail the test for being less than 45 percent of the nominal track width. This has resulted in a reduced yield of heads, thereby increasing manufacturing costs.
One way to improve the yields is to change the tests for non-linearity from being based on the reader width to being based on the actual linearity produced by the head. One way to do this is to test the head over a servo field and to measure the linearity of the PES generated by the head.
To perform this test, the head would be placed on a spin-stand tester where it would write a servo field and then read from the servo field to generate the PES. This option is unattractive because spin-stands that are able to write servo fields are extremely expensive and difficult to implement.
In light of this, the art has suggested that the PES linearity could be modeled based on track scan data. Track scan data is determined in a spin-stand tester by writing a single track of data. The head is then moved across the data in a radial direction and the amplitude of the read signal is recorded at each of a set of positions across the track. This provides a read profile that can be used to simulate the read profile that would be read from servo bursts in the servo field. By combining these servo burst profiles together, a PES model can be generated.
For servo bursts that have a width that is less than the writer width of the head, accurate track scan data can be produced by writing the track and then trimming it to the width of the servo burst. Thus, in drives that use the common ratio of three servo burst widths to two nominal track widths, track scan data can be produced that allows for an accurate estimate of the PES that would be produced by the head.
However, this suggested technique has not been successful at accurately predicting the linearity of the PES generated by a head when the servo bursts have a width that matches the nominal track width. Because of this, it has not been widely adopted in the industry for drives that have such xe2x80x9cone-to-onexe2x80x9d ratios between the servo track widths and the data track widths.
A method and apparatus to qualify heads to be used in disc drives. The method and apparatus collect a set of track scan data by moving the head across transitions in a track on a medium. The track scan data is changed based on a difference between a writer width of the head and a nominal track width to produce modified track scan data. Position error signal data is then determined from at least some of the data in the modified set of track scan data. The linearity of the position error signal data is used to qualify the head.
Additional features and benefits will become apparent upon a review of the following figures and their accompanying detailed description.